1. Field of the Invention
The present invention relates to a driving apparatus, an exposure apparatus utilizing the driving apparatus, and a device manufacturing method utilizing the exposure apparatus.
2. Description of the Related Art
A semiconductor exposure apparatus for transferring a pattern formed on a reticle onto a substrate, such as a wafer, onto which resist is applied, is used in a lithographic process for manufacturing devices such as semiconductor devices and liquid crystal display devices.
Japanese Patent Application Laid-Open No. 2004-254489 discusses a stage apparatus for positioning a wafer and a reticle at predetermined places in an in-plane direction. FIGS. 14A and 14B illustrate a planar motor type stage apparatus discussed in Japanese Patent Application Laid-Open No. 2004-254489. This stage apparatus includes mover magnets 114 and a stator 100. The mover magnets 114 are arranged periodically in a plate-like surface of a mover 110 and are magnetized in a predetermined direction. The stator 100 includes stator coils 116 arranged in an arrangement cycle corresponding to that of the mover magnets 114. The stage apparatus further includes an electric current control unit (not shown) that supplies electric currents, which differ in phase from one another, to the stator coils 116 to generate a driving force for driving the mover 110 between the mover magnets 114 and the stator coils 116 facing the mover magnets 114.
The stator coils 116 are constructed by providing a plurality of layers in each of which substantially oval coils are arranged in a plane. Each of the coils is shaped into an oval. A large number of coils are arranged in a plane. Thus, the mover 110 can have a desired stroke.
Mirrors (not shown) for detecting the position and attitude of the mover 110 are provided on the side surface and top surface of the mover 110. The position and attitude of the mover 110 in the directions of six degrees of freedom can be measured using, e.g., a laser interferometer. A driving force is controlled based on the measured values. Thus, the positioning of the mover 110 in six degrees of freedom can be controlled.
Recently, there have been increasing demands not only for achieving high positioning accuracy in a stage unit of an exposure apparatus to cope with micropatterning but for achieving a high acceleration of the stage unit to increase productivity. One method for achieving a high acceleration is to increase electric current applied to a stator coil. However, when electric current to be applied to the stator coil is increased, the power consumption of the stator coil considerably increases as Joule heating of the coil.
A method for cooling coils made of a normal conduction material, such as copper, to a low temperature in order to reduce electric resistance and a method for using a superconductive material, whose electric resistance is extremely low at a low temperature, as a material of coils are considered as methods for reducing the power consumption. For example, the electric resistance of copper at a liquid nitrogen temperature is reduced to about 1/10 in comparison with the electric resistance at normal temperature. Thus, the power consumption in the case of applying the same amount of electric current to the coils can be reduced to about 1/10.
Japanese Patent Application Laid-Open No. 2004-235653 discusses an apparatus and a method for supporting coils to be cooled to a low temperature. As illustrated in FIG. 15, the apparatus discussed in Japanese Patent Application Laid-Open No. 2004-235653 includes a superconducting coil 201 and a container 205, which surrounds the superconducting coil 201 and maintains the inside thereof in a vacuum condition. This apparatus further includes a magnetic shield 230, which surrounds the container 205, and an adjustment mechanism 241, which adjusts the positional relationship between the magnetic shield 230 and the superconducting coil 201 by adjusting the relative position of the magnetic shield 230 with respect to the container 205.
In the case where a coil to be cooled to a low temperature is used in an exposure apparatus, it is necessary to consider at least the following respects concerning a method for supporting the coil.
First, even when the coil is thermally contracted, sufficient positional accuracy of the entire coil should be satisfied. When the positional accuracy of the coil is degraded, variation in driving force occurs. Thus, the positioning accuracy of a stage maybe adversely affected. In the case where the coil is cooled again after the temperature of the coil is returned to normal temperature in a state in which the coil is cooled for maintenance, sufficient reproducibility of the position of the coil is needed.
According to the method discussed in Japanese Patent Application Laid-Open No. 2004-235653, after the coil is thermally contracted, the coil is supported by pushing adjustment screws against both sides of the coil. Consequently, the positioning of the coil can be achieved using the adjustment screws without forcedly suppressing the thermal contraction.
In the apparatus discussed in Japanese Patent Application Laid-Open No. 2004-235653, when a radiation shield is thermally contracted by cooling the coil, the radiation shield may fail to contact the adjustment screws. Accordingly, when the position of the coil is adjusted, it is necessary to adjust the position of the coil after the adjustment screws are brought into contact with the radiation shield each time when the coil is cooled.
However, because the adjustment of the position of the coil is performed each time when the coil is cooled, it is difficult to restore the position of the coil to the same position each time when the coil is cooled.